Enlargement photography



July 29, 1952 TROUP 2,605,447

ENLARGEMENT PHOTOGRAPHY Filed July 17, 1950 2 SHEETSSHEET 1 FIG- 2 INVENTOR.

J. H. TROUP BY ATTORNEY y 29, 1952 J. H. TROUP ENLARGEMENT PHOTOGRAPHY 2SHEETSSHEET 2 Filed July 17, 1950 FIG. 4

INVENTOR.

J. H. TROUR ATTORNEY Patented July 29, 1952 UNITED STATES PATENT OFFICEENLARGEMENT PHOTOGRAPHY John H. Troup, Harrisburg, Pa. Application July17, 1950, Serial No. 174,277

8 Claims. 1

This invention relates to photography and more particularly to themaking of enlarged photographic prints from negatives.

In making photographic enlargements the negative is placed in anenlarging projector which is adapted to be adjusted the desired distanceabove the surface on which the printing paper is placed. A light sourceis positioned above the negative and the lens below in order to focusthe light rays passing through the negative onto the paper. The degreeof enlargement is a function of the height of the negative above thepaper, the lens aperture influencing the intensity and depth of theimage, and the length of time in which the light rays fall on the papergoverning the exposure time. It has been found that the factorsmentioned are so inter-related that a change in one usually requires achange in one or more of the others. In practice, therefore, asubstantial amount of trial and error technique is employed inorder toachieve the best results. This technique is further complicated by thefact that negatives vary in density, som transmitting light more easilythan others. A still further factor is the processing conditions.However, these may be controlled and maintained relatively uniform.

In the contact printing of negatives, the negative is placedsubstantially in contact with the paper in orderto make a print of thesame scale as the negative. It will b understood, therefore, that incontact printing certain factors present in enlargement printing,including the height of the negative above the paper and the apertureopening, are eliminated. Thus, the only remaining factors, except forthe processing conditions, which w assume to be constant, are theexposure time and the negative density. In contact printing, therefore,an operator of only small experience may by inspection determine theapproximate density of a given negative and adjust the exposure timeaccordingly. Due to the other variable factors encountered inenlargement printing, however, even an experienced operator mustexperiment to arrive at a trial and error solution of the bestcombinationof the variables.

Accordingly, it is an object of this invention to provid a method ofenlargement photography by which the determination of th variablesaffecting the process is greatlysimplified.

A further object of this invention is to provide a method and apparatusfor enlargement photography in which one or more of the variable factorsis automatically determined and the photographic enlarging mechanismautomatically adjusted accordingly,

These and other objects of the invention become apparent from thefollowing description taken in conjunction with the accompanyingdrawings in which:

Fig. 1 is an elevation of enlarging apparatus adapted for carrying outthe present invention;

Fig. 2, a diagram of a bridge circuit for determining the value of oneor more unknown variables.

Fig. 3, a schematic diagram of apparatus including an electrical circuitfor determining and governing the exposure time automatically; and

Fig. 4, a schematic layout of another form of apparatus including anelectrical circuit for determining and governing exposure timeautomatically.

In enlargement photography the equation E =it shows the relationshipbetween E, exposure, i, intensity, and 15, time. However, the basicvariable factors influencing exposure which are encountered in actualpractice, are (1) distance from the negative to the paper, (2) aperture,(3) the printing speed of the negative, and (4) the time of exposure.The exposure given the pap-er is proportional to the product of thesefactors when they are expressed in terms of intensity and time, but theamount of exposure required by the paper in order to produce a properimage is of course dependent on the emulsion and its processing. We hallsee later how it is possible to determin by test the value of thisexposure required. From the above considerations, it is apparent thatthree factors in actual practice determine the value of i in Equation(1) we have,

where i1 is proportional to the intensity of light at the paper as thenegative to paper distance is varied and the two other intensityfactors, aperture and negative printing speed, are held constant; i2 isproportional to the intensity of the light at the paper as theaperturesize is varied, and the distance from negative to paper and the negativeprinting speed are held constant; and i3 is proportional to theintensity of the light at the paper due to a variation in the printingspeed of negatives while the remaining two variables are held constant.We may now combine Equation (1) and Equation (2) as follows:

log E: log i1+log iz+log i3+log t This equation provides a useful toolin solving for the variables in enlargement photography. In order toapply it easily the physical scales on the enlarger are laid out inunits corresponding to the logarithmic units in the above formula.

Referring to the drawings and particularly Fig. l, enlargement apparatusis shown including a base i9 having an upstanding member ll connectedthereto carrying an adjustable arm l2 to which is connected an enlargingcamera or projector l3. The projector has a housing I4 for the lightsource, and a bellows portion [5 by means of which the focal distance ofthe lens carrying member !6 may be adjusted. Slot 1! is providedintermediate of the housing and bellows portion for receiving a negativeto be enlarged. A suitable timing device I8 is shown for receiving powerthrough line l9 and sending it for predetermined intervals through line29 to the source of light within the housing.

Applied to the upright member ll is a scale 25 on which divisions aremarked corresponding to the log ii. Similarly, a scale 22 on the lensaperture mounting ['6 has markings corresponding to the log is and scalereadings 23 on the face of the timer I8 corresponding to the log t. Thescales may be most readily constructed from basic mathematicalconsiderations although a photometer at the paper surface measuring theintensity of the projected light as each variable,

is varied separately would serve as well for constructing scales 2! and22. The log of the photometer intensity readings need only be placed onthe scale positions to which they correspond.

The time scale 23 is either exactly the log of time or it may vary fromthis slightly when a careful worker wishes to compensate for thereciprocity law failure. When the scales are to be con structedmathematically it can be shown that where A is the aperture size, asindicated by focal ratio and 2'2 is proportional to the intensity oflight on the paper surface as A is varied.

In order to enlarge negatives according to my invention, a givennegative, which is preferably although not necessarily of averagedensity, is enlarged by the conventional trial and error technique andis assigned an arbitrary number, such as 3 (log i3 3), this negative nowproviding a standard by means of which other negatives may be rated. Wethen add the number which this negative has been assigned to the readingof the scales 2 I, 22 and 23 to determine their sum, which sum is equalto log E. This quantity is, of course, a measure of the sensitivity ofthe paper used and it will be influenced by the processing conditions aswell as by the emulsion. Then in order to have the proper exposure forthe sam negative but with one or more of the other factors changed, forexample, the negative to paper distance (hence magnification), it isonly necessary to vary one or more of the other factors so that the sumis the same.

If a different negative is to be used, the operator, by comparison withthe standard negative, may judge whether more or less exposure isrequired and the approximate degree thereof, in the same manner as withcontact printing. Thus, by the use of my method, enlargement printing ismade substantially as simple as contact printing. It is, of course,apparent that once a given negative is rated, the need for further trialand error adjustment is eliminated, as it is only necessary to adjustthe other factors such that all factors including the negative ratingnumber total the proper sum.

Although it is not essential to an understanding of this invention, itis contemplated that various modifications may be made in the scales tocompensate for changes in the factors involved from simplerelationships. For example, the time scale 23 may be modified tocompensate for the failure of the reciprocity law by so arranging thescale that the indicator is opposite log t at a certain point and thatall other points indicate log t plus or minus a small correction equalto the increase or decrease in log it necessary to produce a constantdensity as t is varied.

It is, of course, within the contemplation of the invention that othervariables may be included in the equation and determined by suitablemeans. For example, if the voltage for the light source is not constant,it may be determined and included as a factor.

Instead of solving the basic equation mentally or on paper, aconventional bridge circuit may be employed, as shown in Fig. 2, inwhich the fixed resistances 25 and 26 are employed on two legs of thebridge, a variable resistance 21 on a third leg, and variableresistances 28, 29, 39 and SI on the fourth leg. A galvanometer 33 isconnccted across the bridge by conductor 32. Suitable leads 34 and 35extend from the opposite sides of the bridgev to a power source 36. Inoperation the resistances 21, 28, 29, 30 and 3| may be set to correspondrespectively to the variable factors log E, log 2'1, log it, log is andlog t, respectively. Thus, in order to solve the equation for any givenset of variables, after once determining log E, the other variableswould be set into the corresponding resistances until the meter 33 gavezero reading, at which point the bridge would be balanced and the valuesto which the various scales would be set could then be read from thecorresponding resistances.

Instead of reading certain of the values from the scales on the enlargerand setting these in the Wheatstone bridge and solving for the unknownor unknowns by manipulation of the resistances of the bridgecorresponding to the unknown or unknowns, the invention contemplates thedoing of this automatically by providing resistance or rheostat unitswith the scales of the device such that a setting of the various scalesof the device would automatically set corresponding resistances of abridge.

One specific embodiment of the invention whereby the length of time orexposure setting is automatically controlled, is shown diagrammaticallyin Fig. 3. The apparatus illustrated in Fig. 3 comprises asynchronousmotor All which is adapted to drive shaft 42 through a gear re ductionbox 41, the speed of the motor and the reduction gearing ratio beingsuch that the time required for one revolution of the shaft 42 is asgreat as the maximum exposure time contemplated. Attached to the otherend of shaft 42 is one member 43 of a magnetic clutch 44, the field orsolenoid of the magnetic clutch being indicated at 45. The other member46 of the magnetic clutch is connected to shaft 41 which drives themovable member 40 of a variable impedance 49. Connected to the shaft 41is a spiral return spring 50 which is adapted to return the shaft 41 andthe impedance member 48 to its initial position when torque is not beingtransmitted through the magnetic clutch. The impedance 49 is soconstructed that the angular distance through which the shaft 41 turnsis proportional to the log t, or in other words, is proportional to thelog of the exposure time.

The electrical circuit of Fig. 3 includes a Wheatstone bridge havingfixed impedances or resistances 5|, 52 and 53 on three of its legs andvariable resistances 54, 55, 56 and 51 on the fourth leg, leads 58 and59 extending from the fourth leg to the impedance 49 in order that theimpedance be included in series in the leg. The variable resistances 54,55 and 56 correspond respectively to the variable factors log E, log i1,and log is, the impedance 49 corresponding to the factor log t. Insteadof placing the resistance corresponding to the log E in another leg, asthat in Fig. 2, for convenience sake, it is placed in the leg with theother variable resistances, and corresponds to the resistance 51, itbeing understood that the value of the respective variable resistancesmust be proportioned according to the value of the resistances in theother less and to each other.

Instead of employing a meter to indicate the balance of the bridge, asin Fig. 2, or in conjunction therewith, if desired, a coil 60 of a relay6| is connected by leads 62 and 63 to the opposite sides of the bridge.One of the contacts 64 of the relay (H is connected by condutcor 65 toone side 66 of a power line. The other contact 61 of the relay isconnected by lead 68 to a contact 69 of relay 10, relay including a coil1I. One lead 12 of the coil H is connected to the other side 13 of thepower line and the other lead is connected by lead 14 to a contact ofthe relay, and to a contact 16 adapted to engage a contact member orbutton 11. From the button 11 lead 18 extends to the line 66. One of theother contact members 19 of the relay 10 is connected to the line 13.The engaging contact 80 is connected to a line 8| extending to coil 45,the other end of the coil being connected by a conductor 82 to line 66.

A light source 83 in the enlarging projector has leads 84 and 84'connected to lines 8| and 66, respectively. Branching from the line 84is a conductor 85 leading to one of the electrical connections of themotor 40, the other side of the motor being connected directly to thepower line 66.

In the operation of the above circuit the variable resistances 54, 55,56 and 51 are set in accordance with their predetermined values, thevalue of the resistance 51 corresponding to the log E, which isdetermined as previously set forth. The apparatus is then adjusted sothat the negative to paper distance and the aperture opening arecorrect. Then, the apparatus being in readiness, the operator pressescontact button 11 to close the circuit through the coil H of relay 10 inorder to close the normally open contacts 19, 80 and 15, 69. Afterrelease of the contact button 11, the circuit through coil H ismaintained as follows: Power line 13, conductor 12, coil 1I, conductor14, contacts 15, 69, conductor 68, contacts 61, 64 conductor 65 back toline 66. So long as the bridge is unbalanced the current flowing tor 4o,conductors s5, s4 and 8|, contacts so, 19'

and-line 13. At the'same time, the field coil of the magnetic clutch 44is energized through the following circuit: Line 66, conductor 82, coil45, conductor BI, contacts 80, 19 and line 18. The light source 89- islikewise energized as follows: Line 66, conductor84, light 83,conductors 84, 8|, contacts 80, 1,9, and line 13.

As soon as the shaft 41 has turned to the extent that the value of theimpedance 49 is suflicient to balance the bridge, currentceases to flowthrough coil of the relay 6|. When this condition is reached, thecontacts 64, 61 separate, thus breaking the circuit to coil H of relay"and releasing the movable contacts associated with relay 10, thusopening the circuits to the motor 40, the coil 45 of the magnetic clutch44, and the light 83. I

Another illustration of the invention in which the exposure time isautomatically governed in accordance with the valuesof the other factorsis shown in Fig. 4. Referring thereto, variable resistances orimpedances 8641.861), 860 and 86d are connected in series to a, directcurrent source 866 and to the drive 81 of a sector or variable lighttransmission disc 81'. The drive 81 for the disc is oi. the deflectionmeter type or galvanometer, i. e., the angular displacement isproportional to the current flow therethrough. Thus, the angulardisplacement of the sector disc will vary as a function of the totalvalue of the resistances. The function resistances may be set tocorrespond to the log values ofthe factors heretofore mentioned whichwere set into the impedance bridge previously discussed.

The remainder of the circuit shown in Fig. 4 includes power lines88 and88 to the light 69, and including normally open contacts 90 and 9I ofthe relay 92 in line 88', Relay92has a coil 93 one end of which isconnected to conductor 94 leading to plate 950i vacuum tube 96. Theother end of the coil 93' is connected by conductor 91 through directcurrent source 98 to conductor 99 to the cathode I00 of the tube.

The shell I4 of the enlarger is provided with an aperture I4a throughwhich'a beam of light from the light source 89 may be transmittedthrough filter IM and sector disc 81' onto phototube or cell I02. Thephototube I02 is of the type which transmits current therethrough as afunction of the intensity of the light falling thereupon. In otherwords, its efiective resistance decreases as the intensity of the lightit receives increases. The cathode I03 of the phototube is connected inseries with a source of direct power I04 and by conductors I05 and 99 tocathode I00 of the vacuum tube 96. A branch conductor I08 extends fromthe conductor 99 to a condenser I09 in series with the anode I I0 of thephototube I02. Branch conductor III, which is connected to the line I09between the condenser and the member'I I0, is attached to the grid II2of the vacuum tube, a manually depressible contact member H8 beingconnected across conductors I08 and I II in orderto bridge these whendesired.

In order to operate the apparatusjust described, log values ofthefactors, except expo- 7 sure. time, s are set into. thecorrespondingresistancs 8668617, 8611 and 8.60. The. operator thendepressesthe contact l|3 which discharges, condenser I09 to permit flowthrough vacuum tube 95 and. con 93;. offrlay 92 toclosecontacts 9B and 9II oftlie'relay and' permit the light as to be energised. The chargingrate of the condenser H39 a fterrelease. of, contact. I l 3 'iscontrolled by the amount of-olight rfepeived bythe phototube from, thelight summer thesector'disc 8 1 the transmissioii'of lightoithefs'ectordisc being determin'ed' byfits' angular displacement, as determined. by.heftotal resistance of the variable resistances; Wnenenargin hasprogressed such that the negative potentialiof the grid l2,of the vacuumtiibfef 95, reduces the current flowing through the coil9,3 of ,1 relayQ2 below a critical valu'ef'the, contactsf9ll a'ndfS l there-oi open thecircuit tofthelight 89 x Amon the advantages of. this arrangement isthat voltage variationsjare compensated for automatically by variationsin the output, of the lights'oiirce 8'9.

' While an, embodiment of theinvention described in connection withFigs. 3 andehaye, for illustrative purposes, been described @for usewith apparatus 'for automatically determining and controlling the. timeexposure, factor, the invention contemplatesthatthe other factors aswell may be suitably controlled. 'Itis apparent that thefcon'trolir Fig;3 could be used for determining' theother unknow'n factors. Furthermore,the control means shown in Fig. 3, centered around the condition ofbalance or unbalance of the Wheatston'e bridge, could easily be used tocontrol means such as a motor for automatically adjusting the exposuretimeaperture size, or other variables. i

It 'will'be obvious to those skilled in the art that. various. changesI'naS be, mad in this inventioiiwithou't departingirom' the spirit andscope thereof and, therefore, the inventionis not limited to that whichis showninthedrawings and described in the specification, but only asindicatedin the appendedclaims." f

' What is ola'iimed i'stf V I 1. Aii'apparatus for controlling thelength'of time that current news to a source of light, comprisinga'wheatstone bridge having a plurality of variable impeaaseesmne of whichmay be varied by meaastra shaft turned by a motor, saidmotorfhrivi'ngfsaid'shaftthrough a gearreduot'ion means"anramagneueclutch means, magnetic cluteh means; said motor, "and said lig it source-each'havi n g atfleast one circuit-comleting lead in" series with anormally open relay,- unbalance resporisivemeans for" the Wheatstonebridge" for holding.' closed'a normally open circuit to s aidirelay, andmeans for initially closing the ci'rcuit to 's'aid'relayfwherebyafter'initial closing oi the circuit to said relay the magnetic clutch,the motor, and the light source will be energized, the motor rotatingtheshaft and varying the one variable impedance until the VVheatstonebridge is balanced, the means holding the normallyopen circuitto-th'e relay-closed being de-en ergized when 'this cor'idition occurs.

2. An apparatus for controlling the length of time that current flows ina'c'irc'uitcontrolling a variable factorof a photogra'phic"enlarger,comprising a Wheatstiin'e' triage having a plurality of variableimt'eaaiieesyd'ne dffwliich may be varied by means of a'shaftturned bya'm'otor, saidcircuit for controlling the variable factor having a. e itg nerat d in Series with a ace-riser contact of a first pole of a doublepole single throw normally open relay, unbalance responsive means forthe Wheatstone bridge for holding closed a normally open circuit to acontactof a second pole of said relay, means for initially actuatingsaid relay for closing said first and second poles, one of said poles ofsaid relay being in series with the coil thereof whereby the relay maybe initially closed and will remain closed until the unbalanceresponsive means of the Wheatstone bridge causes itto open.

3. An apparatus for controllingthe time interval that current flows. toa light source, comprising a deflection meter in circuit with one ormore variable impedances and a power source, the deflection of the meterbeing governed by the impedance in circuit therewith, the impedancebeing a function of the desired time interval, a variable lighttransmission disc connected to the meter such that its angulardeflection is proportional to the desired time interval, the lightsource being positioned to transmit, light through the variabletransmission disc, a light responsive cell positioned to receive lightfrom the light source through the variable transmission disc, a lead forthe light source having a normally open relay in circuit therewith, acondenser in circuit with the. light responsive cell and with a sourceof power, a multiple-element,vacuum tube having the control for thenormally open relay in its plate circuit, one side of the condenserbeing connected to th grid and the, other to the cathode of the vacuumtube, manually operable means for shunting the condenser, whereby upontemporarily shunting the condenser the plate circuit of the vacuum tubeoperates the relay to close the circuit to the light source, and uponrelease of the shuntingmeans the condenser charges at a rate controlledby the amount of light received by the cell through the variabletransmission disc, the plate current falling below the requiredamountjtomaintain the relay closed when the condenser acg uires a predeterminedcharge.

4. An apparatus for controlling the time interval that current flows toa light source, comprising a deflection meter in a first circuit withmeans responsive to factors governing the time interval, a variablelight transmission disc connected to the meter such that its angulardeflection is a function of the time interval, the light source beingpositioned to transmit light through the variable transmission disc,means positioned to receive light from the light source passing throughthe variable transmission disc and to vary the flow of current in asecond circuit, a lead for the light source having normally opencontacts in series therewith, a condenser in the second circuit, a thirdcircuit comprising the plate circuit of a multiple element vacuum tubeand having means for closing the normally open contacts, the condenserbeing connected to the grid andthe cathode of the vacuum tube, and meansfor shunting the condenser whereby upon shunting the condenser the platecircuit may close the normally open contact to the light source topermit the second circuit to charge'the condenser upon opening theshunting means and whereby the plate circuit will cease to hold open thenormally open contacts upon a predetermined charge being established onthe condenser.

5. An apparatus for controlling the length of time that current flows ina first circuit controlling a variable factor of aphotographic enlarger,

comprising a plurality 'oivariable impedances connected in a secondcircuit to a circuit controlling means indicative of the sum of theimpedances, manually operable means for initiating flow in the firstcircuit, said manually operable means simultaneously initiating flow ina third circuit, the flow in said third circuit being determined by thecircuit controlling means, and means for interrupting flow in said firstcircuit, said means being controlled by flow in saidthird circuit.

6. An apparatus for controlling a photographic operation comprising alight source and means to supply power to said light source, a Wheastonebridge having a plurality of variable resistances in one leg thereof, amotor for varying one of said variable impedances, a manual switch forinitiating operation of said motor, means controlled by a condition ofunbalance of said Wheatstone bridge for continuing the supply of powerto said motor, said means becoming inoperative upon said Wheatstonebridge becoming balanced to stop the supply of power to said motor, saidmeans also controlling the supply of power to said light source wherebywhen said motor stops said power to said light source is stopped.

'7. An apparatus for controlling the exposure of a photographic materialcomprising, a Wheatstone bridge, a plurality of variable impedances inone leg of said bridge corresponding to variable factors of photography,an electric motor for controlling the operation of one of said variableimpedances, an electric light for exposing the photographic material, asource of electricity, circuits connecting the source of electricity,said light source, and said motor for operating the same, manual switchmeans for initiating operation of said motor and said lightsimultantously a source of electricity for said Wheatstone bridge, acoil connected to said Wheatstone bridge and 10 actuated by a conditionof unbalance of said bridge, a normally open switch operated by saidcoil for controlling the flow of electricity to said motor and saidlamp, and means to return said motor operated resistance to initialcondition upon stoppage of said motor and lamp.

8. An apparatus for controlling a photographic operation comprising amotor, a solenoid operated clutch driven by said motor, and a variableimpedance controlled by said clutch, a lamp, and a source of electricalenergy, a circuit for supply- -ing electrical energy to said motor, lampand said clutch, a Wheatstone bridge having said variable impedance inone leg thereof, a source of electricity for said bridge and a solenoidcontrolled switch controlled by said bridge in response to a conditionof unbalance of said bridge, said solenoid controlled switch being incontrol of said motor, lamp, and clutch, and a manual switch forinitiating the operation of said motor, clutch and lamp, said solenoidcontrolled switch thereafter controlling the circuits to stop saidmotor, render said clutch inoperative, and shut off said lamp after'apredetermined interval, and means to return said variable impedance toits starting condition.

JOHN H. TROUP.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,930,137 Twyman Oct. 10, 19332,090,825 Anthony Aug. 24, 1937 2,143,692 Haar Jan. 10, 1939 2,149,250Bing Mar. '7, 1939 2,201,606 Bing May 21, 1940 2,434,157 Hcppeard Jan.6, 1948

